// -*- mode:c++; tab-width:2; indent-tabs-mode:nil; c-basic-offset:2 -*-
/*
 *  BitSource.cpp
 *  zxing
 *
 *  Created by Christian Brunschen on 09/05/2008.
 *  Copyright 2008 Google UK. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <zxing/common/BitSource.h>
#include <sstream>
#include <zxing/common/IllegalArgumentException.h>

namespace zxing {

    int BitSource::readBits(int numBits) {
        if (numBits < 0 || numBits > 32 || numBits > available()) {
            std::ostringstream oss;
            oss << numBits;
            throw IllegalArgumentException(oss.str().c_str());
        }

        int result = 0;

        // First, read remainder from current byte
        if (bitOffset_ > 0) {
            int bitsLeft = 8 - bitOffset_;
            int toRead = numBits < bitsLeft ? numBits : bitsLeft;
            int bitsToNotRead = bitsLeft - toRead;
            int mask = (0xFF >> (8 - toRead)) << bitsToNotRead;
            result = (bytes_[byteOffset_] & mask) >> bitsToNotRead;
            numBits -= toRead;
            bitOffset_ += toRead;
            if (bitOffset_ == 8) {
                bitOffset_ = 0;
                byteOffset_++;
            }
        }

        // Next read whole bytes
        if (numBits > 0) {
            while (numBits >= 8) {
                result = (result << 8) | (bytes_[byteOffset_] & 0xFF);
                byteOffset_++;
                numBits -= 8;
            }


            // Finally read a partial byte
            if (numBits > 0) {
                int bitsToNotRead = 8 - numBits;
                int mask = (0xFF >> bitsToNotRead) << bitsToNotRead;
                result = (result << numBits) | ((bytes_[byteOffset_] & mask) >> bitsToNotRead);
                bitOffset_ += numBits;
            }
        }

        return result;
    }

    int BitSource::available() {
        return 8 * (bytes_->size() - byteOffset_) - bitOffset_;
    }
}
